Lady Gaga herself was on hand to celebrate the opening of her holiday collaboration with the iconic department store. Gaga was decked out for the occasion in a white Chanel gown that was customized by Karl Lagerfeld. There are tons of details about Lady Gaga's Barneys workshop — the installation, which takes over the shop's entire fifth floor, included eight shopping stations customized by Gaga and her team. Fans can browse a jewelry nook, a bookstore, and a boudoir that sell over 170 limited-edition Gaga-themed products as well as some of her favorite items from childhood. The store-within-a-store is open now and will be until Jan. 2, 2012.